In recent years, in order to deal with higher pin counts, fine pitches, and increase in signal speed of semiconductor chips, there are used semiconductor devices employing flip-chip connection as a mounting method having short wiring and connection lengths. When the flip-chip connection is applied to connection between semiconductor chips and connection between a semiconductor chip and a silicon interposer, solder bumps are formed on electrode pads of upper and lower chips (semiconductor chips or silicon interposers) respectively, the chips are aligned to face these solder bumps and stacked, and then the solder bumps are heated and melted to be connected.
In order to remove oxide films on the solder bumps, normally, fluxing agent is coated on the surfaces of the solder bumps, and then the upper and lower chips are aligned and stacked. Next, in a reflow chamber, the solder bumps are heated and melted to be connected, and then the fluxing agent is cleaned. However, in accordance with decreasing size and formation pitch of the solder bumps, it becomes difficult to clean the fluxing agent completely. A residue of the fluxing agent results in a problem.
Thus, it has been considered that the solder bumps are heated and melted to be connected while removing the oxide films on the surfaces of the solder bumps by a carboxylic acid such as a formic acid. In JP-A 2001-244618 (KOKAI) and JP-A 2001-244283 (KOKAI), it has been disclosed that in a state where a semiconductor chip having solder bumps is mounted on a wiring substrate, the semiconductor chip is disposed in a reduced pressure atmosphere containing a carboxylic acid gas, and the solder bumps are heated and melted in such an atmosphere. By heating the solder bumps in the reduced pressure atmosphere containing the carboxylic acid gas, the oxide films on the surfaces of the solder bumps are removed, and voids inside the solder bumps (solder layers) ascribable to gas to occur at the time of heating the solder are removed.
When solder bumps provided on upper and lower chips are connected each other, the solder bumps are temporarily tacked, and then the chips having the temporarily tacked solder bumps are disposed inside a reflow chamber. In this case, the oxide films are caught in interfaces between the temporarily tacked solder bumps, and it is difficult to achieve both improvement in connectivity between the solder bumps and suppression of voids to occur inside the solder bumps after being melted.